The present invention relates to an electrophotographic recorder which is capable of handling various information, such as image information, and the like, and in particular it relates to an optical scanning apparatus which can form a high precision electrostatic latent image on a photosensitive body.
Most of the optical apparatuses for use in conventional electrophotographic recorders adopt an arrangement in which a laser beam reproduced from a single laser source carries out one-dimensional scanning via a single optical system. However, there is disclosed in J-P-A Laid-open Nos. 2-179603 and 4-305612, an arrangement in which, through light emission modulation control of a single emission source, each of a P wave and an S wave of a laser beam therefrom is caused to carry different information, then the laser beam, of which the P wave or S wave is caused to change its polarization direction by a polarization direction shift means consisting of a PLZT element, is directed along a path including a polygon mirror, an F-.THETA. lens and a polarizing beam splitter (PBS) in which the laser beam is split into two beams, each of which expose a photoconductor or photosensitive body.
According to the foregoing arrangement, a laser beam from the F-.THETA. lens enters the polarizing beam splitter at an incident angle which changes in dependence on the scanning position, however, no particular attention has been paid to the influence of the incident angle of light on the polarized light. That is, when each of two polarized beams which are orthogonal to each other is caused to carry individual information, and a PBS is used as a means to split the beam according to each polarization state, the polarization coordinate system which determines oscillatory directions of polarization for the P wave and S wave in dependence on an incident angle with respect to the polarizing beam splitter is caused to rotate. Thereby, when the coordinate system on the incidence side is assumed to be stationary, there results a misalignment between the coordinate systems of the P and S waves due to the changing incident angles. Thus, there occurs a distortion in an emitted light due to this misalignment between the coordinate systems, which in consequence prevents a laser beam printer from generating a high precision latent image in the process of forming an electrostatic latent image with such a laser beam.